Everyone is different. I had no problems with pre- op diet, other than missing food! Know that I am on post op, the protein drinks make am nauseated. Keep your chin up, the time will go by fast.
It was normal for me. On day 3 I was curled in a fetal position in bed for a good part of the day. For me it was the withdrawals from carbs, sugars, and caffeine I'm sure. By day 4 it was better by one week it was great. Detoxing sucks.
Hang in there! You CAN do this. I had some shakiness and horrible headaches. After the first couple of days (day 2 was my hardest) it was smooth sailing.
I am on a pre-op liquid diet as well. Have you checked your sugar level? I was doing that and my sugar kept dropping to the low 70 and 80. My PCP pulled me off all my sugar pills and it has been better since then.
I am on day 6 of my preop diet. I have been keeping busy and making sure to get my protien shakes in at regular times so that I don't get too hungry. But I have been hungry the whole way through. Good luck!!